Internal combustion engines, such as the turbocharged diesel engines used for rail locomotives, require cooling systems to limit the temperatures of various engine components. Internal combustion engines are known to be designed with internal cooling passages for the circulation of coolant to remove heat energy from the engine components. Lubricating oil which is circulated throughout the engine to reduce friction will also absorb heat and, therefore, will also require cooling to avoid reaching temperatures that would detrimentally affect its lubricity. Diesel engines often utilize turbochargers to increase power by compressing the intake combustion air to a higher density. Such compression results in the heating of the combustion air, which must then be cooled prior to its use to enable the engine to have high volumetric efficiency and low emissions of exhaust pollutants. For mobile applications such as rail locomotives, the only readily available heat sink is the surrounding ambient air. It is known to utilize a pumped cooling medium, such as water, to transport heat to finned radiator tubes. The radiator tubes then transfer the heat to the ambient air, often using forced convection provided by fans.
It is often desirable to maintain an internal combustion engine and its associated intake combustion air at multiple different temperatures in order to optimize the performance of the engine. Consequently, coolant at one temperature may be provided to the cylinder jackets of a turbocharged diesel engine and coolant at a lower temperature may be provided to an intercooler for cooling the compressed combustion air. Such a system may use a single pump, heat exchanger, and temperature control valve to accomplish the dual cooling objectives.
Other turbocharged diesel engine cooling schemes may use a subcooler in addition to a radiator. The subcooler is typically located upstream of the radiator in a flow of cooling ambient air. For locomotive applications, ambient air flowing through the radiators is normally provided by a multi-speed fan, since the radiators are positioned on the roof of the locomotive. The use of a subcooler provides a greater temperature difference capability between the temperature of the engine and the temperature of the combustion air.